ISP port blocking practice

Doug Barton dougb at
Fri Sep 3 22:41:53 UTC 2010

On 9/3/2010 3:19 PM, John R. Levine wrote:
> I know people at large ISPs with actual data.  Port 25 blocking is quite
> effective.

Well no one has said it in this thread yet, so I guess it's my turn. :)

When talking about spam it often happens that people make statements 
along the lines of, "Spam still exists, therefore $FOO is not an 
effective countermeasure." I chose to respond to this message to say 
that this line of thinking is flawed because this message (to some 
degree at least) demonstrates that blocking 25 outbound IS effective 
(again, to some degree); which leads to my larger point. There is no one 
magic bullet for spam. It's a hydra of a problem if there ever was one, 
and _every_ option needs to be weighed, both the costs and the benefits. 
I know that a lot of you know this, but the consistent repetition of the 
same logical fallacy just gets under my skin, and like I said, it was my 


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